FEC coding provides for correction of errors in communication signals. Higher coding gains provide for correction of more errors, and can thereby provide for more reliable communications and/or allow signals to be transmitted at lower power levels.
The Optical Transport Hierarchy (OTH), for example, is a transport technology for the Optical Transport Network (OTN) developed by the International Telecommunication Union (ITU). The main implementation of OTH is described in two recommendations by the Telecommunication Standardization section of the ITU (ITU-T), including:
Recommendation G.709/Y.1331, entitled “Interfaces for the Optical Transport Network (OTN)”, December 2009, with an Erratum 1 (May 2010), an Amendment 1 (July 2010), and a Corrigendum 1 (July 2010); and
Recommendation G.872, entitled “Architecture of optical transport networks”, November 2001, with an Amendment 1 (December 2003), a Correction 1 (January 2005), and an Amendment 2 (July 2010).
G.709 defines a number of layers in an OTN signal hierarchy. Client signals are encapsulated into Optical channel Payload Unit (OPUk) signals at one of k levels of the OTN signal hierarchy. An Optical channel Data Unit (ODUk) carries the OPUk and supports additional functions such as monitoring and protection switching. An Optical channel Transport Unit (OTUk) adds FEC coding. Optical Channel (OCh) signals in G.709 are in the optical domain, and result from converting OTUk signals from electrical form to optical form.
FEC coding as set out in G.709 provides for 6.2 dB coding gain. ITU-T Recommendation G.975.1, entitled “Forward error correction for high bit-rate DWDM submarine systems”, February 2004, proposes an enhanced FEC coding scheme with improved coding gain.
Further improvements in coding gain, without impractical additional processing resources, remain a challenge.